“Oasis in the desert” — a particularly rich fossil assemblage from the fossil-poor Szeged Dolomite Formation, Üllés (Szeged Basin, Hungary)
Abstract
The dark grey, brecciated dolomite, which is classified in the Szeged Dolomite Formation, is the most characteristic Mesozoic formation in the Szeged Basin. The representative feature of the formation is the pervasive dolomitization and recrystallization, which accounts for the poor preservation and low specimen number of fossils. This work is a report on the results of a study of an exceptionally rich and well-preserved fossil assemblage. In the thin sections of the Üllés–18 well (Core #6), besides a Hoyenella–Glomospirella–Glomospira-dominated foraminifer assemblage, algae colonies and ostracod double shells were also observed. The special nature of the sample was given by a juvenile specimen of a Megalodontidae (Bivalvia). The carbonate microfacies and fossil assemblage indicate Middle Triassic (Upper Anisian – Ladinian), shallow, backreef-lagoon environments and waters of elevated salinity during the deposition. This high salinity seawater could have played a role in the near-surface dolomitization of the formation.
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